<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta content="width=device-width, initial-scale=1.0" name="viewport">
    <title>Grid Button</title>
    <style>
        body {
            margin: 0;
            /*padding:5px;*/
            height: 100vh;
            display: flex;
            flex-flow: row;
        }
        body div {
            border: 1px solid rgb(73, 180, 64);
        }
        .container {
            flex:1 ;
            display: flex;
            flex-flow: row wrap;
            padding:10px;
        }
        .container-item {
            flex: 1;
            display: flex;
            font-size: 16px;
            padding: 5px;
        }
        button {
            flex:1;
        }
    </style>
</head>
<body>

<div class="container">
    <div class="container-item">
        <button>Click Me</button>
    </div>
</div>

</body>
</html>